The consecutive radiometric titration of several elements with the sodium salt of 1-dithiocarboxy-3-methyl-5-phenyl-pyrazoline containing sulphur-35

T&mm.

1961. Vol. 8. pp. 492 to 496.

Porgamon

Press Ltd.

Printed

in Northern

Ireland

THE CONSECUTIVE RADIOMETRIC TITRATION OF SEVERAL ELEMENTS WITH THE SODIUM SALT OF I-DITHIOCARBOXY-3-METHYL-5-PHENYLPYRAZOLINE CONTAINING SUL~HUR-35~ A. I. BUSEV and V. M. BYR’KO~ State University M. V. Lomonosov, Moscow, U.S.S.R. (Received 17 January 1961. Accepted 7 Febrmry 1961) Summary-The possibility has been demonstrated of the consecutive radiometric titration of a number of combinations of elements, such as Tlru-Inin, Tim--Znrl and Cdn-Zn**. New forms of radiometric titration curves have been obtained. ORGANIC precipitants containing radioactive isotopes deserve a more widespread application than they receive at the present time. We have used with success for this purpose the sodium salt of l-dithiocarboxy-3-methyl-5-phenylpyrazole, C,,H,sN,S2Na :

cH’~~GHs &SNa

Like the derivatives of dithiocarbamic acid studied earlier, the sodium salt of I-dithiocarboxy-3-methyl-5-phenylpyrazole is capable of forming sparingly water-soluble compounds with a series of elements of the hydrogen sulphide and ammonium sulphide groups. The difference in the behaviour of the metal compounds formed is explained both by their dissimilar solubilities and by the dissimilar stabilities of the tartrates or other complexes of the metals at various pH values of the solution. By making use of this state of affairs it is possible to determine consecutively a series of elements simultaneously present by radiometric titration according to the precipitation method, unique titration curves being obtained. In this paper some examples are presented of the consecutive titration of two ions, of which one is completely precipitated from tartrate solutions at pH - 14 and the other is precipitated only at lower pH values. EXPERIMENTAL Apparatus and reagents The sodium salt of l-dithiocarboxy-3-methyWphenylpyrazole was synthesised by the method reported earlier,’ starting from the corresponding pyrazole and carbon disulphide containing sulphur35 with a specitic activity of 13 mcjml. The preparation obtained had a high specific activity which ensured an activity of about 1000 countsjmin in the sample taken in the titration. Freshly prepared solutions were always used. Before dissolution, the reagent was dried in a desiccator over phosphorus * Translated from IVsh, Khim. i Khimxheskaya Technologiya, 1960, 3, No 1, 52. t Student D. B. Sibiryakova took part in this work. 492

Consecutive

radiometric

titration

of several elements

493

pentoxide. The normality of the solution was 0.01295N calculated from the weight of reagent taken The activity was measured with a type B and 0.0129ON according to a thallium111 salt determination. instrument with a SBT-8 end-window tube. Before measuring the activity with respect to the yradiation of zinc-65, an ahuninium filter with a thickness of ~2 mm was placed in front of the window. The equivalence point was found graphically. The solutions of thallium-204 and of stable thallium were prepared by dissolving the metals in oguu regiu; then thallium111 hydroxide was precipitated, washed several times with water and dissolved in HNO,. The other solutions were prepared by dissolving the appropriate metals in nitric acid. Titration of thalliumIII and indium”‘: Into a centrifuge tube with a capacity of 50 ml were introduced a predetermined volume of titrated solutions of thalliumlI1 and indiumrn, a few ml of a 1% solution of NH&l, an excess of a 5 ‘A aqueous sodium tartrate solution, and NaOH until the indicator tropeolin-00 changed to red or in an amount 1000

250

0

0.5

I.5

I.0 ml

of

2.0

2.5

reagent

FIG. I.-Curves for the consecutive radiometric titration of a 0.0044Nsolution of thalliumnr and a 0.0045~~ solution of indiumlll with a 0.05N solution of I-dithiocarboxy-3-methyl-5phenylpyrazoline sodium salt containing sulphur-35: 1, titration of thallium; 2, titration of indium. previously calculated to bring the pH to 14. The reagent solution was added from a 5-ml burette in separate portions; after separation of the precipitate by centrifuging, 0.01 ml of the solution was taken with a micropipette, deposited on filter paper and dried under an infrared lamp, and its activity was measured. In spite of the soft B-radiation of sulphur-35 (Eg = 0.1691 MeV), there was no need to introduce a correction for self-absorption. Since the sample taken was not put back, the amount of the ion being determined diminished somewhat during the titration, but since the volume of the solution titrated was relatively large (lo-20 ml) and a minimum amount of solution was taken in the titration, the relative error does not exceed 1% which, in comparison with the error of the radiometric titration of +5x, has little influence on the final results. Until the end-point of the titration is reached, the activity of the solution above the precipitate will be determined by the solubility of the thallium compound formed. After all the thallium has been precipitated, the activity of the solution increases with the addition of the reagent (Fig. 1, curve 1). The completion of the reaction is also clearly observed visually from the cessation of the formation of the yellow precipitate of the thallium compound. On subsequent acidification of the solution to pH N 7 by the addition of acetic acid, with continuous agitation, the white indium compound begins to precipitate. On further addition of the reagent, the precipitation of the indium compound proceeds and the activity of the solution will be determined by the solubilities of the thallium and indium compounds. After all the thallium has been precipitated, the activity of the solution rises again (Fig. 1, curve 2). The results of the titration are given in Table I. Underfavourable conditions itis possible, in principle, to titrate the ions of three metals successively.

A. I. BUSBVand V. M. BYR’KO

494

Titration of thallium111and .zirS Curves of a different type are obtained in the titration with a labelled reagent of two ions of which the one precipitating at the higher pH itself contains a radioactive isotope. As an example we shall consider the titration of thalliumln and zinc .I1 The titration procedure was the same as in the previous case. To a standard solution of thalliumln was added an amount of the radioactive isotope *‘JaTl,such that the activity of the sample taken in the titration was lOOO-12OOcpm. On addition of the reagent, the activity of the solution above the precipitate will fall in consequence of the formation TABLE

I.

TITRATIONOF

THALLIUMIII AND INDIUM~IIW~H

I-DITHIOCARIjOXY-3-METHYL-5-PHENYLPYRAZOLINE

THESODIUM

CONTAINING

SALT OF

SULPHUR-35

In added,

In found,

mg

W

0.50 3.00 2.00 1.50

0.46 2.94 2.09 1.43

Error, % -8@O -2.00 $4.50 -4.67

2000

1500

.E E \ u) ; 3

1000

,"

500

0

I.0

mL of reagent FIG. 2.-Curves for the consecutive radiometric titration of a O.OlN solution of noaTllu and a 0.01 N solution of zinc with a @OSN solution of I-dithiocarboxy-3-methyl-S-phenylpyrazoline sodium salt containing sulphur-35: 1, titration of thallium; 2, titration of zinc

of the sparingly soluble thallium compound; after reaching the equivalence point, the activity of the solution will rise because of the activity of the reagent (Fig. 2, curve I). After lowering of the pH, the excess of reagent added will react with the zinc ion, and the activity will be determined by the solubility of the two precipitates containing the isotopes B”*Tland Y3. After the equivalence point is reached, the activity rises and will be determined by the activity of the reagent (Fig. 2, curve 2). Titration of cadmium” and zim+ When the cation precipitating second itself contains a radioactive isotope a somewhat different form of curve is obtained on titrating a mixture of cations with a labelled reagent. This situation

Consecutive radiometric

495

titration of several elements

exists, for example, in the titration of solutions of cadmium and zinc containing the isotope &&Znwith a solution of a labelled reagent. As can be seen from curve I, Fig. 3, as the cadmium precipitates the activity in the solution remains constant and depends on the radiation of the 86Zn. After precipitation of all the cadmium and acidification of the solution to pH 7, the slight excess of reagent introduced reacts with the zinc and the activity of the solution above the precipitate diminishes. A decrease in TABLE II. TITRATION 0~ THALLI~M-~O~II~ AND ZINC WITH THE SODIUM SALT OF I-DITHIoCARBoXu-3-METHYL-5-PHENYLPYRAZOL

Tl added, mg 3.0 3.0 3.0 6.0 9.0 3.0

I .-

Error, %

Tl found, mg

CONTAINING

Zn found,

W

mg

-~

3.3 6.6 9.9 3.3 3.3 1.5

/

I

0.5

0

I.0

SULPHUR-35

Zn added,

I.5

3.5 6.9 9.5 3.4 3.4 1.4

~

2.0

Error, %

-I

+ 6.06 + 4.54 -4.05 f 3.03 + 3.03 -6.67

2.5

mL of reagent FIG. 3.-Curves

for the consecutive radiometric titration of a 0405N solution of zinc-65 and a 0405N solution of cadmium with a 0.05N solution of I-dithiocarboxy-3-methyl-Sphenylpyrazoline sodium salt containing sulphur-35: 1, titration of cadmium; 2, titration of zinc. TABLE III.

TITRATION OF CADMIUM AND ZINC WITH THE SODIUM SALT OF

I-DITHIOCARBoXY-3-METHYL-5-PHENYLPYRAZOLINE CONTAINING SULPHUR-35

Cd taken,

Cd found,

m?

“K

1 Zn taken, / m?

Error, %

Zn found,

1

%

I .54 1.54 10.40 2.10

1 TABLE~V.

19 14

-11.22 -3.57 -9.53 -3.79

DETERMINATION OF CADMIUM AND ZINC 1~ PHOSPHORS

Found, mean (of 6 titrations), Phosphors

Error,

“‘R

/

~T-;dS

9.62 10.85

%

Total ZnS + CdS in

Zn

!

&.,S

60.52 59.03

/ I

90.17 87.91

(

the phosphorsy76 99.79 98.76

-

496

A. I.

BUSEV

and V. M.

BYR’KO

the activity of the solution will be observed as long as all the zinc has not been precipitated. On addition of an excess of the reagent, the activity of the solution above the precipitate rises (measurement of the p-radiation of the sulphur-35). Thus, curve 2 in Fig. 3 gives the total amount of cadmium and zinc and curve I is a typical curve for a titration by the method of non-isotopic indicators. Results of the determination of various amounts of zinc and cadmium are given in Table III. Zinc and cadmium in phosphors based on ZnS and CdS have been determined in accordance with the methods described above (Table IV). Zusammenfassung-Die Moglichkeiten Kombinationen von Elementen radiometrisch hintereinander zu titrieren werden aufgezeigt, wie z.B. die Systeme Thallium-Indium(III), Thallium(III)-Zink(I1) oder Cadmium(II)-Zink(I1). Neue Formen von radiometrischen Titrations-kurven werden gezeigt. RBsun16-Les auteurs montrent qu’il est possible de doser simultanement par radiometrie des combinaisons d’tlements telles que thallium(III)-indium(III), thallium(III)-zinc(I1) et cadmium(II)-zinc(I1). De nouvelles formes de courbes de titrage radiometriques sont present&. REFERENCE 1 A. N. Kost, A. I. Busev, I. I. Grandberg

and V. M. Byr’ko, NDVSh,

Khim.,

1958, 349.